Glaucoma is caused by a number of different eye diseases that, in most cases, produce increased pressure within the eye. This elevated pressure is caused by a backup of fluid in the eye, and will, over time, cause damage to the optic nerve.
Glaucoma may be treated by medicaments daily in order to down-regulate aqueous humour production or increase outflow of aqueous humour. Alternatively, the glaucoma may be treated by surgery in order to allow for drainage of the aqueous humour and thereby lower the IOP.
Laser surgery (laser trabeculoplasty) is currently the major surgical technique employed. This non-invasive procedure takes between 10 and 20 minutes, is painless, and can be performed in either a doctor's office or an outpatient facility. The intense heat of the laser causes some areas of the eye's drain to shrink, resulting in adjacent areas stretching open and permitting the fluid to drain more easily. Complications are few, which is why this procedure has become increasingly popular.
The major invasive surgical technique is a glaucoma filtration procedure called trabeculectomy. In this procedure, the surgeon makes an opening by removing a small section of the trabecular meshwork, the eye's drain. By penetration of the sclera, the anterior chamber is reached and aqueous fluid can be released to a subconjunctival space. This procedure is usually done under local anaesthesia. In some patients, surgery is about 80-90% effective in lowering pressure. Although trabeculectomy is a relatively safe surgical procedure, about 30-50% of patients develop cataracts within five years of surgery. Approximately 10-15% of patients require additional surgery.
Newer surgical techniques, such as viscocanalostomy and deep sclerectomy, avoid penetration of the trabecular meshwork (D H Johnson and M Johnson, Glaucoma surgery and aqueous outflow: how does non-penetrating glaucoma surgery work?, Arch Ophthalmol (2002) 120(1):67-70). In viscocanalostomy, highly viscous hyaluronic acid compositions are used to prevent healing and postoperative scarring of the channel that is formed within the tissue. This procedure reduces complications seen with trabeculectomy. Viscocanalostomy involves creation of a large scleral flap (after conjunctival opening) of about one third of the scleral thickness: performing a second scleral excision inside the first flap up to a thin scleral layer covering the choroid; preparation of this flap into the roof of Schlemm (unroofing) and into the cornea, thus creating a “Descemet's window”; expanding Schlemm's canal with hyaluronic acid; and suturing of the first scleral flap. The many steps make the procedure difficult and time-consuming.
In a minority of patients, various types of drainage implants, made of inter alia metal, plastics, silicon or collagen, are inserted. These may help avoiding inflammation and scar formation that prevent successful drainage of the aqueous fluid.
Optionally, healing of the created channel and scar formation may be prevented by addition of chemicals, such as Mitomycin C and 5-fluorouracil (5-FU).
US patent application publication 2002/0072673 A1 and U.S. Pat. Nos. 5,360,399 and 6,375,642 B1 are concerned with viscocanalostomy.
U.S. Pat. No. 6,558,342 B1 discloses an intraocular tube, which upon implantation may be used to inject fluid or viscoelastic material into to the anterior chamber or under the conjunctiva.
U.S. Pat. No. 6,142,969 discloses implantation of a fluid shunting device into the anterior chamber. During the procedure, a channel is created, which optionally is filled temporarily with a viscoelastic substance to prevent backflow of aqueous humour before the device is inserted.
U.S. Pat. No. 5,360,425 discloses insertion of a needle to the subconjunctival space and infusion of a fluid, such as sodium hyaluronate. Thereafter, a fistula is created by ablation of the sclera employing laser pulses from an optic fibre.
U.S. Pat. No. 4,955,883 discloses that a fistula can be perpetuated in the sclera using a combination of goniopuncture and cauterisation. During this procedure, the anterior chamber can be filled with a viscoelastic material.
U.S. Pat. No. 4,716,154 discloses that a gel of cross-linked hyaluronic acid can be used as a substitute for vitreous humour. U.S. Pat. No. 5,092,837 discloses that a viscoelastic substance can be instilled in the anterior chamber to prevent collapse during insertion of a permanent implant. U.S. Pat. No. 5,811,453 discloses that injection of viscoelastic materials in the anterior chamber ameliorates inflammatory conditions resulting from glaucoma filtration surgery.
EP 1 129 683 A1 discloses injectable compositions of hyaluronic acid gel which are useful as artificial vitreous bodies. U.S. Pat. No. 5,827,937 discloses a viscoelastic gel comprising cross-linked hyaluronic acid that is useful in eye surgery. WO 98/26777 discloses a composition that is injected into the anterior chamber during eye surgery.
U.S. Pat. No. 6,383,219 discloses an implant made of cross-linked hyaluronic acid, which is useful for deep sclerectomy for draining aqueous humour during surgical treatment of glaucoma.
US patent application publication 2003/0211166 A1 discloses compositions of microspheres formed of cross-linked hyaluronic acid. The compositions are allegedly designed to be injected into Schlemm's canal.
U.S. Pat. No. 6,495,608 and WO 92/00745 discloses injection of a viscoelastic composition into the anterior or posterior chamber, which composition is removed at the end of surgery.
C Raitta et al, Acta Opthalmologica 66:544-551 (1988), discloses subconjunctival injection of cross-linked hyaluronic acid in rabbits without change of IOP.
WO2004/026347 discloses surgical creation of a channel between the anterior chamber and ocular veins in the sclera.
Known invasive treatments have some drawbacks in that they are complicated and time-consuming. Moreover, invasive treatment of glaucoma is not very effective, since the created channels tend to heal and form scars.